Control electronics for large format printer.

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Control electronics for large format printer.

Postby tmccafferty » Fri May 10, 2013 4:43 am

I am beginning a build of a large format printer. I will begin assembly of the mechanical platform this weekend. The print envelope is approximately a 21" cube. I may attempt a build log. I am building it mostly from stuff on hand so it's not likely something someone else woul duplicate, but I do think it has some novel features that may be beneficial or stir creative juices of others.

Anyway, back to topic. I haven't ordered my electronics yet. I am using some larger steppers that I had with standalone driver electronics. Each driver has its own power supply and control. I just need to give it step pulses and direction. I am familiar with ramps 1.4 from my Ord. I was thinking of using one of them or similar. I think it should work to not pulp in the normally used drivers and pick off the step and direction signal for each axis. The newer controllers that have integrated motor drivers would'nt be as convenient. I want 3axis to feed the standalone drivers. I want at least two extruders and for that, I would use the plug in type drivers. So, 5 motor outputs minimum. For the heated bed, I have a 24V @ 25amp power supply. The bed will be an aluminum plate with power resistors on bottom. It will be able to handle almost 500 watts. I will use a 60amp solid state relay between the printer control board and the heaters. I would like outputs for 4 fans and maybe a light if possible.

Anybody see any issues with this approach? Any obvious controllers stand out for the task? I am going to assemble all the electronics inside a nema enclosure. Terminal screw connections would be preferred.
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Re: Control electronics for large format printer.

Postby SystemsGuy » Fri May 10, 2013 11:21 am

Using bang-bang on the bed heater can really cause z-artifacts, as the MM1.5 guys discovered about this time last year - not sure what the solution would be in your case - but I'm sure there's a mosfet that could drive the load - may require a driver but I've not looked to see what logic level 'fets are available these days.

I know of at least one of the H-Bot guys who's using a smoothie to drive external stepper drivers, but I've not see any details - I suspect you are right and with step and direction pins, you can drive it as you like. Unless you already have the externals, I'd look at the SuperSteppers or something based on the TI 8825's that can drive up to 2.5 amps...
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Re: Control electronics for large format printer.

Postby tmccafferty » Fri May 10, 2013 12:23 pm

Thanks for the response. I was planning on connecting the solid state relays input to the MOSFET that normally drives the heater. I assumed the PWM input would be ok for the SSR. Is there some issue with this?
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Re: Control electronics for large format printer.

Postby orcinus » Fri May 10, 2013 1:17 pm

SystemsGuy wrote:Using bang-bang on the bed heater can really cause z-artifacts, as the MM1.5 guys discovered about this time last year


Sorry to barge in, but any more info/details on this?
Thermally or electrically (interference) induced artifacts?
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